Heres an interesting mod you may have heard about. A team of modders is creating the city of New York, a whole bunch of real cars to go with the map, and there's an entirely new storyline and more - all in the San Andreas engine. Check out some of these preview screenshots:

And as all other Full modification mods with this much specs.. It doesn't come out....
Dont get your hopes up guys, there's alot of possibilitie there will be a "problem" (A.K.A They get tired of the game) and the mod never reaches it's beta version. And if it does. It does not even have half of what they promissed.